The present invention relates to maintenance of automatic transmissions, and more specifically, to determining the remaining service life of automatic transmission fluid.
According to the Automatic Transmission Rebuilders Association of Ventura, Calif., over 11 million automatic transmission failures per year (nearly nine out of ten automatic transmission failures) are caused by degradation of automatic transmission fluid due to heat. Heat causes transmission fluid to change its chemical composition, and that compromises its performance and accelerates wear on internal components of automatic transmissions. To prevent such failures, the automatic transmission fluid must be changed before it reaches the end of its service life. This is typically done at periodic intervals, usually based on mileage. For example, the owner manuals of automobiles may recommend changing the automatic transmission fluid every 30,000 miles.
However, a number of factors, such as transmission temperature, ambient temperature, coolant temperature, number of shifts, and the like, actually determine the service life of automatic transmission fluid. Therefore, the service life of automatic transmission fluid can vary from car to car depending on how the car has been driven, and the climate and geographic conditions in which it has been driven. For example, the automatic transmission fluid in a car driven mainly on the freeway at a steady speed in a temperate climate will have a longer service life than the automatic transmission fluid in a car driven under severe driving conditions. In the former case, the automatic transmission fluid may well have a significant amount of its service life left at the end of the periodic mileage interval, whereas in the latter case, its service life may have been exceeded.
The remaining service life of transmission fluid is generally evaluated by an automotive technician based on the smell of the fluid and its visual inspection. An overheated transmission will burn the fluid resulting in a recognizable odor. However, it is hard to accurately determine the remaining service life of automatic transmission fluid based on its appearance and smell.
Accordingly, it would be desirable to create a device for determining the remaining service life of automatic transmission fluid.
The present invention offers a novel method of determining the remaining service life of automatic transmission fluid (ATF). The method involves emitting radiation in the direction of an ATF sample under test. The opacity of the ATF sample is measured based on the radiation passed through the ATF sample. The remaining service life of the ATF is determined as a function of the measured opacity.
Preferably, a signal indicative of the opacity may be compared with multiple calibration levels to determine the remaining service life of the ATF under test. Each of the multiple calibration levels may be established based on the intensity of radiation passed through the ATF having known length of life.
For example, the ATF sample may be irradiated with infrared radiation to provide consistent indication of the remaining service life for ATF of various types. Alternatively, the ATF sample may be irradiated with red light to increase the accuracy of determining the remaining service life of ATF as a function of the measured opacity.
In accordance with one aspect of the present invention, a system for testing ATF comprises a radiation source for emitting radiation in the direction of the ATF sample under test, a radiation receiver responsive to the radiation for producing an output signal representing the intensity of radiation passed through the ATF sample, and an output circuit responsive to the output signal for measuring the opacity of the ATF.
In an embodiment of the present invention, the output circuit is configured to compare the output signal with multiple calibration levels to provide a multiple level indication of the remaining service life of the ATF. Each of the calibration levels corresponds to the output signal of the radiation receiver produced in response to the radiation passed through the ATF having known length of life.
For example, each of the calibration levels may be maintained at the same level for testing ATF of any type. In this case, a source of infrared radiation is a preferable radiation source, because it provides more consistent indication of the remaining service life for various types of ATF.
Alternatively, the calibration levels may be set for testing ATF of a particular type. In this case, a source of red light is a preferable radiation source because it increases the accuracy of determining the remaining service life of ATF.
The ATF sample under test may be contained in a disposable container to prevent contamination of the testing system by previously tested ATF. A narrow slot may be provided between the radiation source and the radiation receiver for receiving the disposable container.
A radiation controller may be provided for controlling radiation emitted by the radiation source. The radiation controller may control the radiation source to make the intensity of the emitted radiation sufficient to traverse the ATF sample under test. For example, the radiation controller may control the radiation source so as to emit a predetermined sequence of radiation signals with progressively increasing intensity.
Still other aspects of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein an embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.